Magnetic recording media



Nov. 3, 1959 D. GABOR MAGNETIC RECORDING MEDIA Filed Aug. 19, 1957 INVENTOR DENNIS GABOR B Wfia, 44$M HIS ATTORNEYS United States Patent MAGNETIC RECORDING MEDIA Application August 19, 1957, Serial No. 679,003

'11 Claims. (Cl. 117-7) The present invention relates to magnetic recording mediaand more particularly to a new and improved recording medium of the type comprising a plastic filament carrying permanent magnet material.

It has been proposed heretofore to use as a recording medium a filament made of plastic material and coated with a suspension of a permanent magnet powder of the type commonly employed in magnetic tapes. Such filamentary recording media have not been found satisfactory for the reason that when spooled, the magnetizable coating on each filament below the top layer is in intimate contact with the coatings on six adjacent filaments. This results in a strong print through effect in which there is unwanted copying on each filamentary coating of the modulation patterns in each of the other filamentary coatings with which it is in intimate contact. Whereas, in coated tapes, the thickness of the support separating the magnetic coatings greatly reduces the tendency to print through, at least for the shorter wavelengths, say less than about four times the tape thickness, in the case of coated filaments or threads there is no lower limit to the wavelengths which will print through, and the printing eifect of the longer wavelengths is also enhanced.

It is an object of the invention, accordingly, to provide new and improved filamentary recording media of the above character that are free from the above-noted deficiencies of the prior art.

Another object of the invention is to provide new and improved filamentary recording media of the above character in which the permanent magnet coating has a direction of easy magnetization at an angle to its longitudinal axis.

A further object is to provide a novel method and apparatus for the fabrication of filamentary recording media according to the invention.

In accordance with the invention, a filamentary support made of plastic material is provided with a coating incorporating anisotropic magnetic material, i.e., a maguetic material having a preferred direction of easy magnetization, the direction of easy magnetization being disposed at an angle, preferably in the vicinity of 45, to

the longitudinal axis of the support. When a filament of this type is wound on a spool, the directions of easy magnetization in any two adjacent coatings which are in contact will be at right angles to one another. Consequently, the two coatings will have little remanent effect on each other, and such effect as there may be will be reversible and will vanish as soon as the two adjacent turns of the recording medium are separated.

The invention also contemplates the provision of a novel method for fabricating filamentary recording media of the type described above. It comprises generally the steps of coating a plastic filament with a suspension of anisotropic magnetic material in finely divided form;

twisting the coated filament-so that a straight generating line on the surface of the coating and parallel to the longitudinal axis is twisted into a helix; subjecting the coated twisted filament to a strong magnetic field directed longitudinally of the filament to position the particles of magnetic material so that their directions of easy magnetization are disposed longitudinally of the filament; untwisting the coated filament to position the magnetic particles with their directions of easy magnetization at an angle to the longitudinal axis; and applying heat to the coating to harden the same and fix the magnetic particles in their last-named positions.

For a better understanding of the invention, reference is made to the following detailed description of several representative embodiments thereof, taken in conjunction with the accompanying drawings in which:

Fig. 1 is a perspective view of apparatus suitable for fabricating filamentary recording media of the type shown in Fig. 2;

Fig. 2 is a schematic diagram in perspective of a piece of a filamentary recording medium constructed according to the invention;

Fig. 3 is a view in transverse section taken along the line 33 of Fig. 2 and looking in the direction of the drawings;

Figs. 4A and 4B illustrate difierent ways in which a filamentary recording medium according to the invention may be twisted during the fabrication thereof; and

Fig. 5 illustrates schematically a modification of the apparatus shown in Fig. 1.

Fig. 1 shows one form of apparatus suitable for fabricating filamentary magnetic recording media according to the invention. It comprises a pair of similar supporting heads 10 and 10a mounted in spaced apart relation on suitable standards 11 and 11a. Since the heads 10 and 1011 are substantially identical in construction, it will be necessary to describe only one in detail and corresponding parts of the other will be designated by like reference numerals with the subscript letter a.

The supporting head 10 comprises three wheels 12, 13 and 14 lying in planes disposed, say, apart and intersecting at the longitudinal axis of the apparatus. Formed in the peripheries of the wheels 12, 13 and 14 are annular grooves 15, 16 and 17, respectively. The wheels 12, 13 and 14 are mounted on shafts 18, 19 and 20, respectively, which are journaled in bearings formed in substantially U-shaped brackets 21, 22 and 23, respectively, secured to a ring-like housing 24. The adjacent peripheral portions of the wheels 12, 13 and 14 cooperate to grip a filamentary magnetic record element 25 firmly as shown in Fig. 3, while allowing easy progress thereof in the longitudinal direction.

Disposed between the fixed supporting heads 10 and 10a is a rotatable twisting head 26 which is provided with clamping means 27 enabling it to be clamped in different angular positions. The clamping means 27 comprises a bracket 28 carried by a standard 29 to which a clamp 30 is adapted to be secured by means of a screw 31, for example.

The twisting head 26 also carries three Wheels 32, 33 and 34 which are also mounted, say, 120 apart. However, the peripheries 35, 36 and 37 of the wheels 32, 33 and 34, respectively, are preferably cylindrical surfaces concentric with the wheels or only slightly grooved so as to establish good contact with the surface of the filament or thread 25. Also, the wheels 32, 33 and 34 are rotatably mounted in U-shaped brackets 38, 39 and 40 which are secured to a ring-like member 41 concentric with the thread 25 by a plurality of threaded pins 42, 43 and 44 and bolts 45, 46 and 47, respectively.

Between the fixed supporting head 10 and the twisting head 26 is disposed a conventional magnetizing element 48 which is positoned to subject the thread or filament 25 to a strong magnetic field directed longitudinally there- ,of. Also, between the twisting head 26 and the fixed supporting head a is disposed an electric oven 49 of conventional type which is suitably designed to generate heat to solidify the thermo setting binder in the coating on the. filament or thread and at the same time to speed up the elastic relaxation of the base material of which the thread 25 is formed.

The thread 25 comprises a base 50 preferably made of a plastic material such as nylon which has the property of so-called elastic memory, i.e., when heated after deformation beyond the elastic limit, it returns to its initial undeformed state. Other materials having this property are known to the art and several other specific examples are disclosed in the Patent No. 2,566,441 to Camras. Over the base 50 is a coating 51 which may comprise, for example, high polymeric resinous material having embodied therein fine particles of ,ferro-magnetic material having a preferred direction of easy magnetization. Coatings of this type are well known.

In one way of fabricating a filamentary record medium according to the invention, a thread or filament 25 as described above, with the coating 51 in the soft state, is threaded through the stationary head 10, the magnetizing head 48, the twisting head 26, the oven 49 and the stationary head 10a. It is now firmly gripped by the wheels in the supporting heads 10 and 10a which are supported in the position shown. The wheels 32, 33 and 34 of the twisting head 26 are positioned to an angle of say 45 relatively to the longitudinal direction and are maintained fixed in this position by tightening down the screws 45, 46 and 47, respectively. With the screw 31 loosened, the ring-like member 41 is rotated in a clockwise direction until a generatrix in the surface of the coating 51 on the filamentor thread 25 is twisted into a helix having a 45 elevation angle as illustrated in Fig. 4A. In this figure, the points where the heads 10, 26 and 10a, respectively, grip the thread 25, are represented by the letters A, B and C.

The thread 25 is now advanced longitudinally through the heads 10, 26 and 10a by conventional means (not shown). It will be observed that because of the angular position of the wheels 32, 33 and 34 of the twisting head 26, the thread or filament 25 will be rotated once for every axial displacement equal to its circumference. As a result, the helical twisting initially applied to the thread or filament 25 between the points A and B in Fig. 4A will be maintained as shown in Fig. 4B. However, the twisting head 26 will simultaneously produce, in the section of the thread 25 between the twisting head 26 and the supporting head 1011, a twist which is opposite to the 45 helical twist initially applied between the points B and C. As a result, the generatrix at the surface of the coating in this section will come out ultimately as a straight line as shown in Fig. 4B.

In passing between the supporting head 10 and the twisting head 26, and while twisted in the form of a helix of 45 elevation angle, the magnetic particles in the soft coating 51 are subjected to a strong polarizing field by the polarizing head 48. This causes the magnetic particles to line up with their directions of easy magnetization in the longitudinal direction. In passing through the oven 49, the thermosetting binder for the coating 51 is solidified so that the polarized particles tend to retain the direction of polarization imparted to them by the polarizing head 48. At the same'time, the heat applied to the thread or filament 25 in passing through the oven 49 facilitates the restoration of the deformed plastic base to its initial undeformed state. When this happens, it will beunderstood that the polarized articles of ferro-ma-gnetic material on the coating 51 will now have their directions of easy magnetization disposed at an angle of 45 to the longitudinal axis as best shown in Fig. 2.

One disadvantage of the apparatus shown in Fig. 1- is that the coating 51 on the base 50 of the filament or thread 25' is soft at the time it passes through the rollers in both the supporting head 10 and the twisting head 26 so that these rollers tend to become coated with the soft coating material. This is avoided in the modification shown in Fig. 5 by interposing a second twisting head 26a of the same general character as the twisting head 26 in Fig. 1 between the twisting head 26 and the supporting head 10a. In this form of the invention, the untwisted base 50 of the thread 25 is fed to the supporting head 10 and to the twisting head26 before the coating is applied thereto. After the base has been twisted to the desired degree, it is coated with a suspension of particles of magnetic material in a suitable plastic binder, the magnetic particles are magnetically polarized and the coating is then solidified by a conventional coating applicator 52, a polarizing head 48 and an oven 49, respectively, all interposed between the twisting heads 26 and 26a. A second oven 29a may be interposed between the second twisting head 26a and the supporting head 10a to apply heat of the proper temperature for a sufficient length of time to enable the deformed coated base to be restored to its initial undeformed condition.

It will be understood that the method and apparatus described above by way of illustration may be modified without departing from the spirit of the invention. For example, the portion between A, and B in Fig, 4B may be twisted to a first helix, say right-handed, as. described above, while the portion between B and C may subse'r quently be untwisted beyond the straight line to a lefthanded helix. This has the definite advantage that the angle of twist need not be as great as in the exemplary technique described above in order to achieve the desired elevation angle of 45 for the axis of easy magnetization of the magnetic particles.

This might be accomplished, for example, by stretching the filament longitudinally during the twisting process and allowing it to relax while it is being untwisted. The number of turns of twist and untwist are necessarily equal and of opposite sign, but the given number of turns will be. distributed over a shorter length in the relaxed part of the filament than in the stretched part. Hence, the

desired final elevation angle of 45 can be achieved with a twist of substantially less than 45 This is an advantage because strongly twisted elastic filaments do notv run straight but tend to form helices or even loops, as is well-known from experience with overwound rubber bands.

It will be apparent from the foregoing description that the invention provides novel and highly effective filamentary' magnetic recording media. By aligning the particles of magnetic material comprising the coating of the filament so that their directions of easy magnetization lie at an angle of, say, 45 to the longitudinal axis. of the filament, the directions of easy magnetization in: any two adjacent filament sections when wound on a spool are at angles to one another so that they will have little permanent effect on one another and there will be only a small tendency to print through from one finam'e'nt portion to another.

The specific apparatus and techniques described above are intended to be merely illustrative, and the invention is not to be limited thereto but is intendedto compreheld all modifications coming within the scope of the following claims.

I claim:

I. A magnetic record medium comprising a filament carrier including binder material incorporating anisotropic ferro-magnetic material having its direction of easy magnetization oriented at an angle to the longitudinal axis of said filament.

2. A magnetic record medium comprising a plastic filament having a coating including binder material incorporating anisotropic ferro-magnetic material havingits direction of easy magnetization oriented at an angle to the longitudinal axis of said filament.

3. A magnetic record medium comprising a filamen made of a plastic material having an elastic memory and a coating of finely divided particles of anisotropic ferromagnetic material in a binder, said particles of magnetic material having their directions of easy magnetization oriented at an angle to the longitudinal axis of said filament.

4. In a method for fabricating a magnetic record medium, the steps of providing a filament of plastic material, twisting a portion of said filament between spaced apart locations therealong, applying to an anisotropic ferro-magnetic material incorporating in a binder on said filament twisted portion a polarizing magnetic field di rected along the longitudinal axis of said filament, to polarize said anisotropic ferromagnetic material with its direction of easy magnetization along said longitudinal axis, heating the filament, and untwisting it so that the direction of easy magnetization lies at an angle to the longitudinal axis of the filament.

5. A method as defined in claim 4 together with the step of affixing said anisotropic ferromagnetic material to said filament portion in said polarized position.

6. A method as defined in claim 5 in which thefila ment portion is untwisted to its initial position and then twisted in the opposite direction to establish the desired angle between the direction of easy magnetization of the magnetic material and the longitudinal axis of the filament. s

7. A method as defined in claim 5 in which the filament portion is stretched longitudinally during the twisting thereof and is allowed to relax during the untwisting thereof.

8. .In a method for fabricating a magnetic record medium, the steps of providing a filament of plastic ma terial having an elastic memory and coated with finely divided particles of anisotropic magnetic material in a thermosetting plastic binder, twisting a portion of said filament between spaced apart locations therealong, applying to said particles of magnetic material a polarizing magnetic field directed along the longitudinal axis of said filament, heating said filament portion to set said plastic binder with said particles in the polarized position, and restoring said filament portion to its initial untwisted condition.

9. In a method for fabricating a magnetic record medium, the steps of providing a filament of plastic material having an elastic memory, twisting a portion of said filament between spaced apart locations therealong, applying to said filament portion a coating of finely divided particles of anisotropic magnetic material in a thermosetting binder, applying to said particles of magnetic material a polarizing magnetic field directed along the longitudinal axis of said filament, heating said filament portion to set said plastic binder with said particles in the polarized position, and restoring said filament portion to its initial untwisted condition.

10. In apparatus for fabricating a magnetic record medium, the combination of spaced apart support heads for gripping a record medium during the advancement thereof, a twisting head for said record medium, intermediate said support heads, magnetic polarizing means between said twisting head and one of said support heads for establishing a magnetic field in the direction of advancement of said record medium, and heating means between said twisting head and the other of said support heads for applying heat to said record medium.

11. In apparatus for fabricating a magnetic record medium, the combination of spaced apart support heads for gripping a record medium during the advancement thereof, a pair of spaced apart twisting heads interposed intermediate said support heads, means interposed between said twisting heads for coating said record medium with finely divided particles of magnetic material in a binder, and magnetic polarizing means disposed between the pair of twisting heads for magnetically polarizing the coated medium and heat generating means disposed between said twisting heads for heating said coated and polarized record medium.

References Cited in the file of this patent UNITED STATES PATENTS 

8. IN A METHOD FOR FABRICATING A MAGNETIC RECORD MEDIUM, THE STEPS OF PROVIDING A FILAMENT OF PLASTIC MATERIAL HAVING AN ELASTIC MEMORY AND COATED WITH FINELY DIVIDED PARTICLES OF ANISOTROPIC MAGNETIC MATERIAL IN A THERMOSETTING PLASTIC BINDER, TWISTING A PORTION OF SAID FILAMENT BETWEEN SPACED APART LOCATIONS THEREALONG, APPLYING TO SAID PARTILES OF MAGNETIC MATERIAL A POLARIZING MAGNETIC FILED DIRECTED ALONG THE LONGITUDINAL AXIS OF SAID FILAMENT, HEATING SAID FILAMENT PORTION TO SET SAID PLASTIC BINDER WITH SAID PARTICLES IN THE POLARIZED POSITION, AND RESTORING SAID FILAMENT PORTION TO ITS INITIAL UNTWISTED CONDITION. 